This invention pertains to paint coatings and particularly to powder paint coatings based on thermosetting polymeric binders comprising a functional fluorocarbon polymer adapted to be crosslinked with a blocked isocyanate crosslinking resin.
Fluorocarbon polymers dispersed in organic solvents are disclosed in U.S. Pat. No. 3,340,222 and U.S. Pat. No. 3,324,069 although such compositions require considerable amounts of organic solvent which cause undesirable solvent emission problems. Aqueous dispersed polyvinylidene fluoride polymers are disclosed in U.S. Pat. No. 4,022,737 and U.S. Pat. No. 3,770,685 and U.S. Pat. No. 3,679,618 while admixtures of aqueous polymers and acrylic polymers are disclosed in U.S. Pat. No. 4,141,873 and U.S. Pat. No. 4,383,075. However, dispersion of fluorocarbon polymers into water is difficult and paint films produced by polymeric admixture often produced non-uniform and non-homogenous paint films due to discrete particles of high Tg fluorocarbon polymer particles dispersed throughout the paint film which can cause premature failure of the paint film as pointed out in commonly assigned U.S. Pat. No. 4,383,075.
It now has been found that solid functional fluorocarbon copolymers alone or in combination with other functional polymers can be used as binder polymers useful in dry powder paint coatings substantially free of solvents and water. The functional fluorocarbon copolymers are coreactive with crosslinking components and particularly with blocked isocyanates to produce highly desirable thermosetting powder paints which provide protective surface paint films exhibiting considerably enhanced exterior durability as well as improved gloss retention and chalk resistance. Other film integrity properties such as mechanical resilience and salt spray resistance are improved or maintained in comparison to other high quality films based on conventional acrylic or polyester polymers for powder coatings. The use of functional fluorocarbon polymers in powder coatings further eliminates the dispersion problem in solvent or water dispersed coatings and further eliminates dispersion and powder processing difficulties encountered with the use of high Tg, high melt, thermoplastic fluoropolymers in powder coatings. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples.